1. Field of the Invention
The present invention relates to a method of producing a stator blade for use in a turbo-molecular pump for an evacuation purpose, and a turbo-molecular pump having the stator blade.
2. Description of the Related Art
A turbo-molecular pump designed for a high level of evacuation is provided with a plurality of rotor blades arranged in a multistage manner and a plurality of stator blades arranged in a multistage manner. Each of the rotor blades comprises a plurality of blade elements each formed to extend around an entire circumference of a rotor while protruding from an outer peripheral surface of the rotor. Each of the stator blades comprises a plurality of blade elements each arranged to surround the rotor, wherein each of the blade elements is connected to an arc-shaped strip member at an outer peripheral edge surface and/or an inner peripheral edge surface thereof. Generally, the stator blade in each stage is made up of a pair of semicircular-shaped blade segments. Each of the stator blades is disposed between adjacent ones of the rotor blades arranged along an axial direction of the rotor, whereby an evacuation action is produced when the rotor blades are rotated relative to the stator blades at a high speed according to rotation of the rotor.
Heretofore, as a method of fabricating such stator blades, there has been known a technique of subjecting a semicircular-shaped metal plate to a punching process to form a plurality of blade elements each supported by inner and outer peripheral ribs, and subjecting the blade elements to an angling process to obtain a stator blade. In the angling process, each of the blade elements having a rectangular vertical-section is angled and positioned in an obliquely inclined posture. Thus, each of upper and lower edge surfaces of the obliquely-inclined blade element is positioned to have a chevron shape protruding in the axial direction of the rotor, which leads to a problem about an increase in overall size of the pump.
As measures for this problem, there has been proposed a production method designed to slidingly move a punch relative to a plate in an oblique direction during a punching process so as to allow a blade element after being subjected to an angling process to be position to have horizontally-extending upper and lower edge surfaces (see, for example, JP 2003-269365A).
In cases where a metal plate is subjected to a punching process using a punch, a burr is highly likely to be formed during punching, and thereby it is necessary to additionally perform a burr removal operation. If a thicker metal plate is used to ensure the rigidity of a stator blade, a fabrication cost will be further increased. Moreover, in the above method, a desired sliding direction during the oblique sliding movement of the punch is different between a plurality of blade elements to be formed in the metal plate. Thus, it is extremely difficult to form all the blade elements by one cycle of punching operation, which will accelerate an increase in fabrication cost.